GIS crankcase shell low-pressure casting mold and process

Abstract

This application discloses a low-pressure casting mold and process for GIS crankcase shells, relating to the technical field of low-pressure casting of GIS crankcase shells. It includes a metal outer mold assembly and a coated sand core disposed inside the metal outer mold assembly. The metal outer mold assembly includes a lower mold and an upper mold, with side molds on both sides of the lower mold. An ejection mechanism is integrated inside the lower mold. The coated sand core is positioned in a core seat inside the metal outer mold assembly via a core head, forming the internal cavity structure of the casting. The combination of these structures can improve production efficiency, increase the density of the casting, and reduce overall production costs.

Description

Technical Field

[0001] This invention belongs to the field of low-pressure casting technology for GIS crank arm box shells, specifically a low-pressure casting mold and process for GIS crank arm box shells. Background Technology

[0002] As a core device in the power system, GIS (Gas Insulation System) undertakes the critical tasks of power transmission, distribution, and control, and its operational stability is directly related to the safety and reliability of the power grid. The GIS crankcase housing, as a key structural and sealing component within the GIS equipment, not only needs to provide stable installation space for internal components such as bearings and transmission mechanisms, but also must ensure that the insulating gas inside the equipment does not leak, placing extremely high demands on its mechanical properties and sealing performance. However, the internal structure of the GIS crankcase housing is extremely complex, typically containing intricate bearing mounting seats and channels, which presents a significant challenge to its manufacturing process.

[0003] Traditional casting processes have many shortcomings in meeting the requirements of structural complexity and performance, and it is difficult to balance production efficiency, product quality and manufacturing cost. Traditional sand gravity casting or all-sand low-pressure casting processes are also problematic.

[0004] Sand gravity casting involves pouring molten metal into a sand mold under gravity, allowing it to cool and solidify to obtain a casting. However, sand gravity casting has several insurmountable drawbacks:

[0005] 1. Poor internal quality: The poor insulation of the sand mold leads to slow cooling of the molten metal, resulting in a coarse microstructure in the casting and making it difficult to meet design requirements in terms of mechanical properties. Furthermore, relying on gravity filling and natural feeding makes it highly susceptible to defects such as shrinkage cavities, porosity, and gas holes within the casting, affecting the equipment's sealing performance and service life.

[0006] 2. Low production efficiency. Sand molds are disposable consumables, and each casting requires a new sand mold to be made. This is a labor-intensive and time-consuming process with a long production cycle.

[0007] 3. Low dimensional accuracy: Sand molds are prone to deformation during pouring and cooling, and there are slight differences in handmade sand molds, resulting in poor dimensional accuracy of castings and rough surfaces. This requires a lot of grinding and processing steps, which increases production costs and production cycle.

[0008] All-sand low-pressure casting involves introducing compressed air into a sealed crucible, causing molten metal to fill the sand mold cavity from bottom to top under pressure. This process improves the internal quality of castings to some extent, but it still has significant limitations:

[0009] 1. Limited improvement in production efficiency: Although the filling process of low-pressure casting is relatively stable, the production and drying of sand molds still require a lot of time.

[0010] 2. Defects in surface quality and dimensional accuracy: The inherent characteristics of sand molds result in high surface roughness of castings, making it difficult to meet high-precision requirements in terms of dimensional accuracy, and the amount of subsequent machining is still large.

[0011] 3. High overall cost: Although the initial investment cost of sand molds is relatively low, the high scrap rate, low yield, and high post-processing costs of castings result in high overall costs.

[0012] Therefore, we propose a low-pressure casting mold and process for GIS crankcase shell. Summary of the Invention

[0013] The purpose of this invention is to provide a low-pressure casting mold and process for GIS crankcase housing in order to improve production efficiency, increase the density of castings, and reduce overall production costs.

[0014] The technical solution adopted in this invention is as follows:

[0015] A low-pressure casting mold and process for a GIS crank arm box shell includes a metal outer mold assembly and a coated sand core disposed inside the metal outer mold assembly. The metal outer mold assembly includes a lower mold and an upper mold. Side molds are disposed on both sides of the lower mold. An ejection mechanism is integrated inside the lower mold. The coated sand core is positioned in a core seat inside the metal outer mold assembly by a core head to form the internal cavity structure of the casting.

[0016] In a preferred embodiment of the invention, the upper mold is fixed to the press movable plate, and the bottom of the upper mold is provided with a cavity surface that matches the top shape of the GIS crank arm box housing.

[0017] In a preferred embodiment of the invention, the lower mold is fixed to the press worktable, and the top of the lower mold is provided with a cavity surface that matches the bottom shape of the GIS crank arm box housing.

[0018] In a preferred embodiment of the invention, the side mold consists of two movable molds arranged symmetrically on the left and right sides, which can move in the horizontal direction, and the inner side of the side mold is provided with a cavity surface that matches the side structure of the GIS crank arm box shell.

[0019] In a preferred embodiment of the invention, the coated sand core comprises at least one hollow shell sand core manufactured by a thermal core-forming process.

[0020] In a preferred embodiment of the invention, the lower mold, the side mold, and the upper mold are all internally integrated with partitioned cooling water channels, and each cooling water channel is independently connected to an external cooling control system.

[0021] In a preferred embodiment of the invention, a sealing gasket is provided between the core head of the coated sand core and the core seat of the metal outer mold assembly to prevent molten metal from seeping into the core head gap during the filling process and causing the sand core to shift.

[0022] A low-pressure casting process for a GIS crank arm box shell includes the following steps:

[0023] S1. Mold and sand core preparation: Preheat the metal outer mold assembly to 200℃-350℃, spray the mold release agent on the surface of the mold cavity, and at the same time trim the coated sand core for later use.

[0024] S2. Lowering the core and closing the mold: The coated sand core is positioned and installed in the core seat of the metal outer mold assembly through the core head, and the upper mold, the lower mold and the side mold of the metal outer mold assembly are driven to close to form a closed cavity that matches the shape of the GIS crank arm box shell;

[0025] S3. Low-pressure filling: Dry compressed air is introduced into the holding furnace so that the molten metal is smoothly filled into the mold cavity from bottom to top through the riser pipe under a pressure of 0.01MPa-0.07MPa.

[0026] S4. Pressure Holding Solidification and Feeding: After filling, hold the pressure at 0.03MPa-0.07MPa for 60-180 seconds to allow the casting to solidify and feed under pressure.

[0027] S5. Pressure relief and mold opening: After the casting has completely solidified, the pressure is relieved, and the unsolidified molten metal in the riser pipe flows back to the holding furnace, driving the outer metal mold assembly to open the mold, and the casting with the sand core is taken out through the ejection mechanism.

[0028] S6. Sand core cleaning: The removed casting is subjected to vibration or shot peening treatment. The coated sand core will collapse due to resin combustion after high-temperature casting, and the internal cavity of the casting will naturally form. This allows some residual loose sand to flow out and collapse from the inside of the casting and be cleaned out of the inside of the casting, thus obtaining the GIS crank arm box shell casting.

[0029] In a preferred embodiment of the invention, the coated sand core assembly is made of high-strength, low-gas-emission coated sand with a high-temperature tensile strength ≥2MPa and a gas emission rate ≤12mL / g.

[0030] In a preferred embodiment of the invention, during the pressure holding, solidification, and shrinkage compensation step, the solidification sequence is controlled by adjusting the flow rate of the cooling medium in the partitioned cooling water channels within the metal mold outer mold assembly. This increases the cooling flow rate for thin-walled portions of the casting directly formed by the metal mold and reduces cooling for thick, hot-spot portions wrapped by the coated sand core assembly.

[0031] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0032] 1. In this invention, the lower mold, upper mold, and side mold of the metal outer mold assembly are precisely matched with the bottom, top, and side shapes of the GIS crank arm box shell, respectively. The high-precision machining of the cavity surface ensures that the external contour dimensional error of the casting is small and the surface finish is high, reducing the amount of subsequent grinding processing. At the same time, the coated sand core is made by the hot shell core process, which can flexibly form the complex internal bearing mounting seat and channel structure. The sand core is removed by vibration or cleaning after casting. Finally, the casting achieves high quality with metal mold casting on the outside and structure of arbitrary complexity inside, improving production efficiency.

[0033] 2. In this invention, the lower mold, side mold, and upper mold of the metal outer mold assembly are all integrated with partitioned cooling water channels. Each cooling water channel is independently connected to an external cooling control system, which can precisely adjust the cooling rate according to the wall thickness differences of different parts of the casting. For thin-walled parts directly formed by the metal mold, the cooling flow rate is increased to accelerate their solidification; for thick, hot-spot parts wrapped with coated sand cores, cooling is reduced, and the heat insulation properties of the coated sand cores are used to ensure that these parts solidify last. Combined with the continuous feeding pressure of low-pressure casting, sequential solidification of the casting is achieved, effectively avoiding internal defects such as shrinkage porosity and shrinkage cavities, improving the density of the casting, and reducing the risks of "high cooling rate" and "shrinkage porosity in thick parts".

[0034] 3. In this invention, the main structure of the metal outer mold assembly is simple, and the mold opening and closing is fast. With the help of the ejection mechanism, automated part removal can be achieved, ensuring the production cycle. The coated sand core can be quickly manufactured through the hot shell core process, which effectively reduces the complexity and cost of the mold. At the same time, the coated sand core has a certain degree of flexibility at high temperatures. When the casting begins to shrink, the sand core will slightly collapse, giving the casting a certain shrinkage space, reducing the tendency of thermal cracking caused by shrinkage obstruction, and further improving the yield. Through the synergistic effect of the above structures, while maintaining the high efficiency of low-pressure casting of metal molds, complex internal cavities are perfectly formed, achieving a balance between efficiency and complexity, and reducing the overall production cost. Attached Figure Description

[0035] Figure 1 This is a perspective view of the present invention;

[0036] Figure 2 This is a top view of the present invention;

[0037] Figure 3 This is a perspective view from another angle in this invention;

[0038] Figure 4 This is a flowchart of the casting process in this invention.

[0039] The markings in the diagram are: 1-Metal outer mold assembly, 2-Coated sand core, 11-Lower mold, 12-Side mold, 13-Ejection mechanism, 14-Upper mold. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] Example 1:

[0042] Reference Figures 1-4 A low-pressure casting mold and process for a GIS crank arm box shell includes a metal outer mold assembly 1 and a coated sand core 2 disposed inside the metal outer mold assembly 1. The metal outer mold assembly 1 includes a lower mold 11 and an upper mold 14. Side molds 12 are provided on both sides of the lower mold 11. An ejection mechanism 13 is integrated inside the lower mold 11. The coated sand core 2 is positioned in a core seat inside the metal outer mold assembly 1 by a core head to form the internal cavity structure of the casting. The upper mold 14 is fixed to the movable platen of the press, and the bottom of the upper mold 14 has a cavity surface that matches the top shape of the GIS crank arm box shell. The lower mold 11 is fixed to the press worktable, and the top of the lower mold 11 has a cavity surface that matches the bottom shape of the GIS crank arm box shell. The side molds 12 are symmetrically arranged on the left and right sides. Two movable molds can move horizontally. The inner side of the side mold 12 is provided with a cavity surface that matches the side structure of the GIS crank arm box shell. Specifically, the lower mold 11, upper mold 14 and side mold 12 of the metal outer mold assembly 1 are precisely matched with the bottom, top and side shapes of the GIS crank arm box shell, respectively. The high-precision machining of the cavity surface ensures that the external contour dimension error of the casting is small and the surface finish is high, reducing the amount of subsequent grinding. At the same time, the coated sand core 2 is made by the hot shell core process, which can flexibly form the complex internal bearing mounting seat and channel structure. The sand core is removed by vibration or cleaning after pouring. The final casting achieves high quality with metal mold casting on the outside and structure of arbitrary complexity inside, improving production efficiency.

[0043] Example 2:

[0044] Reference Figures 1-4The coated sand core 2 includes at least one hollow shell sand core made by a hot core process; the lower mold 11, side mold 12 and upper mold 14 are all integrated with partitioned cooling water channels, and each cooling water channel is independently connected to an external cooling control system; a sealing gasket is provided between the core head of the coated sand core 2 and the core seat of the metal outer mold assembly 1 to prevent molten metal from seeping into the core head gap during the filling process and causing the sand core to shift; specifically, the lower mold 11, side mold 12 and upper mold 14 of the metal outer mold assembly 1 are all integrated with partitioned cooling water channels, and each cooling water channel is independently connected to an external cooling control system, which can precisely adjust the cooling rate according to the wall thickness difference of different parts of the casting. For thin-walled sections directly formed by metal molds, the cooling flow rate is increased to accelerate solidification; for thick, hot sections wrapped by coated sand core 2, cooling is reduced, and the heat-insulating properties of the coated sand core are used to ensure that these sections solidify last; combined with the continuous feeding pressure of low-pressure casting, sequential solidification of the casting is achieved, effectively avoiding internal defects such as shrinkage porosity and shrinkage cavities, improving the density of the casting, and reducing the risks of "high cooling rate" and "shrinkage porosity in thick sections".

[0045] Example 3:

[0046] Reference Figures 1-4A low-pressure casting process for a GIS crankcase shell is described. During mold and sand core preparation, the metal outer mold assembly 1 is preheated to 200℃-350℃, and a release agent is sprayed onto the mold cavity surface. Simultaneously, the coated sand core 2 is prepared for use. During core lowering and mold closing, the coated sand core 2 is positioned in the core seat of the metal outer mold assembly via a core head, driving the upper mold 14, lower mold 11, and side mold 12 of the metal outer mold assembly 1 to close, forming a closed cavity matching the shape of the GIS crankcase shell. During low-pressure filling, dry compressed air is introduced into the holding furnace, causing the molten metal to be at a pressure of 0.01MPa-0.07 MPa. Under pressure of MPa, the mold cavity is smoothly filled from bottom to top through the riser pipe; during pressure holding, solidification, and feeding, after filling, the pressure is held at 0.03MPa-0.07MPa for 60-180 seconds to allow the casting to solidify and feed under pressure; after depressurization and mold opening, the pressure is released after the casting has completely solidified, and the unsolidified molten metal in the riser pipe flows back to the holding furnace, driving the metal outer mold assembly 1 to open the mold, and the casting with sand core is taken out through the ejector mechanism 13; sand core cleaning, the removed casting is vibrated or shot peened, and the coated sand core 2 will collapse due to resin combustion after high-temperature pouring, and the internal cavity of the casting will naturally form The mold is formed by allowing some residual loose sand to flow out and dissipate from the inside of the casting, thus cleaning out the interior of the casting and obtaining the GIS crankcase shell casting. The coated sand core assembly is made of high-strength, low-gas-emission coated sand with a high-temperature tensile strength ≥2MPa and a gas emission ≤12mL / g. In the pressure holding, solidification, and feeding steps, the solidification sequence is controlled by adjusting the cooling medium flow rate of the partitioned cooling water channels inside the metal mold outer mold assembly. The cooling flow rate is increased for thin-walled parts of the casting directly formed by the metal mold, and the cooling is reduced for thick, hot-spot parts wrapped by the coated sand core assembly. Specifically, the main structure of the metal outer mold assembly 1 is simple, and the mold opening and closing is fast. The ejection mechanism 13 enables automated part removal, ensuring production cycle time. The coated sand core 2 can be quickly manufactured using the hot core process, effectively reducing mold complexity and cost. At the same time, the coated sand core 2 has a certain degree of flexibility at high temperatures. When the casting begins to shrink, the sand core will slightly collapse, providing the casting with some shrinkage space, reducing the tendency for thermal cracking caused by obstructed shrinkage, and further improving the yield. Through the synergistic effect of the above structures, while maintaining the high efficiency of low-pressure casting of metal molds, complex internal cavities are perfectly formed, achieving a balance between efficiency and complexity, and reducing overall production costs.

[0047] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0048] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A low-pressure casting mold for a GIS crank arm box shell, comprising a metal outer mold assembly (1) and a coated sand core (2) disposed inside the metal outer mold assembly (1), characterized in that: The metal outer mold assembly (1) includes a lower mold (11) and an upper mold (14). Side molds (12) are provided on both sides of the lower mold (11). An ejection mechanism (13) is integrated inside the lower mold (11). The coated sand core (2) is positioned in the core seat inside the metal outer mold assembly (1) through the core head to form the inner cavity structure of the casting.

2. The low-pressure casting mold for a GIS crank arm box shell as described in claim 1, characterized in that: The upper mold (14) is fixed to the press movable plate, and the bottom of the upper mold (14) is provided with a cavity surface that matches the top shape of the GIS crank arm box shell.

3. The low-pressure casting mold for a GIS crank arm box shell as described in claim 1, characterized in that: The lower mold (11) is fixed to the press workbench, and the top of the lower mold (11) is provided with a cavity surface that matches the bottom shape of the GIS crank arm box shell.

4. The low-pressure casting mold for a GIS crank arm box shell as described in claim 1, characterized in that: The side mold (12) consists of two movable molds arranged symmetrically on the left and right sides, which can move in the horizontal direction. The inner side of the side mold (12) is provided with a cavity surface that matches the side structure of the GIS crank arm box shell.

5. The low-pressure casting mold for a GIS crank arm box shell as described in claim 1, characterized in that: The coated sand core (2) includes at least one hollow shell sand core made by a thermal core process.

6. The low-pressure casting mold for a GIS crank arm box shell as described in claim 1, characterized in that: The lower mold (11), the side mold (12) and the upper mold (14) are all equipped with partitioned cooling water channels, and each cooling water channel is independently connected to an external cooling control system.

7. The low-pressure casting mold for a GIS crank arm box shell as described in claim 1, characterized in that: A sealing gasket is provided between the core head of the coated sand core (2) and the core seat of the metal outer mold assembly (1) to prevent the molten metal from seeping into the core head gap during the filling process and causing the sand core to shift.

8. A low-pressure casting process for a GIS crank arm box shell, characterized in that... The method described in any one of claims 1 to 7 is used, and the steps are as follows: S1. Mold and sand core preparation: Preheat the metal outer mold assembly (1) to 200℃-350℃, spray the mold release agent on the surface of the mold cavity, and at the same time trim the coated sand core (2) for later use. S2. Lower core and mold closing: The coated sand core (2) is positioned and installed in the core seat of the metal outer mold assembly through the core head, and the upper mold (14), the lower mold (11) and the side mold (12) of the metal outer mold assembly (1) are driven to close, forming a closed cavity that matches the shape of the GIS crank arm box shell; S3. Low-pressure filling: Dry compressed air is introduced into the holding furnace so that the molten metal is smoothly filled into the mold cavity from bottom to top through the riser pipe under a pressure of 0.01MPa-0.07MPa. S4. Pressure Holding Solidification and Feeding: After filling, maintain pressure at 0.03MPa-0.07MPa for 60-180 seconds to allow the casting to solidify and feed under pressure. S5. Depressurization and mold opening: After the casting has completely solidified, the pressure is depressurized, and the unsolidified molten metal in the riser pipe flows back to the heat preservation furnace, driving the metal outer mold assembly (1) to open the mold, and the casting with sand core is taken out through the ejection mechanism (13); S6. Sand core cleaning: Vibration or shot peening is performed on the removed casting. The coated sand core (2) will collapse due to resin combustion after high temperature casting. The internal cavity of the casting will naturally form, so that some residual loose sand will flow out from the inside of the casting and be cleaned out of the inside of the casting to obtain the GIS crank arm box shell casting.

9. The low-pressure casting process for a GIS crank arm box shell as described in claim 8, characterized in that: The coated sand core assembly is made of high-strength, low-gas-emission coated sand, with a high-temperature tensile strength ≥2MPa and a gas emission ≤12mL / g.

10. The low-pressure casting process for a GIS crank arm box shell as described in claim 8, characterized in that: In the pressure holding, solidification, and shrinkage compensation step, the solidification sequence is controlled by adjusting the cooling medium flow rate of the partitioned cooling water channels inside the metal mold outer mold assembly. The cooling flow rate is increased for the thin-walled parts of the casting directly formed by the metal mold, and the cooling is reduced for the thick, hot-nozzle parts wrapped by the coated sand core assembly.

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